1. Field of the Invention
The present invention relates to a piezoelectric transducer and, more particularly, to a low frequency transducer for the generation and/or reception of torsional shear waves.
2. Description of the Related Art
Shear waves are transversely propagating waves that can only be supported in an elastic media. Examples of such media are solid and semisolid materials, such as ocean floor sediment. Water does not support the propagation of shear waves because it is a fluid.
In geological surveying and ocean bottom profiling, among other fields, there is a need for measuring the degrees of support and energy dispersion for shear wave propagation. In particular there is a need to measure the sound speed and attenuation of shear-wave propagation in the media at sonar frequencies. The information provided by these measurements can result in improved understanding of a media. This is particularly important for low frequency propagation and the effects that the media can introduce to the propagation and acoustic wave energy.
More particularly, improved sonar equipment can be developed if it is more accurately known how shear waves move through sediment. Further, oil exploration efforts can better locate shale deposits and oil if shear wave movement can be more fully qualified. Also, it is beneficial to be able to monitor shear wave movement through ocean sediment after an earthquake on the ocean floor. It is also desired to detect to extent of shear wave propagation caused by underwater explosions.
The present technique for measuring geo-acoustic properties has been shear wave generation resulting from underwater explosions. This technique is costly and has significant environmental drawbacks. Also, it is difficult to obtain repeatable results or quantitative and qualitative studies.
Other transduction methods have included a bimorph piezoceramic transducer that generates shear waves along a single plane. This type of transducer is quite fragile and is of limited use in low frequency, higher power transmitting applications.
Thus, although means currently exist for measuring the degrees of support for shear wave propagation, they fail to provide the most effective, economical and easy to use transducer. A need therefore exists for an improved shear wave transducer.